Method of etching and method of plasma treatment

ABSTRACT

A processing gas constituted of CH 2 F 2 , O 2  and Ar is introduced into a processing chamber  102  of a plasma processing apparatus  100 . The flow rate ratio of the constituents of the processing gas is set at CH 2 F 2 /O 2 /Ar=20 sccm/10 sccm/100 sccm. The pressure inside the processing chamber  102  is set at 50 mTorr. 500 W high frequency power with its frequency set at 13.56 Mz is applied to a lower electrode  108  on which a wafer W is placed. The processing gas is raised to plasma and thus, an SiN x  layer  206  formed on a Cu layer  204  is etched. The exposed Cu layer  204  is hardly oxidized and C and F are not injected into it.

TECHNICAL FIELD

The present invention relates to an etching method and a plasmaprocessing method.

BACKGROUND ART

As ultra high integration in semiconductor devices increasing in recentyears, manufacturing superfine metal wirings that conform to rigorousdesign rules has become a crucial technical requirement. However, whenthe aluminum wirings normally utilized in the prior art, such as wiringsconstituted of Al or an Al alloy, are miniaturized, the level of theelectrical resistance becomes significant, which readily causes a wiringdelay, lowering the operating speed of the semiconductor device. As asolution, adoption of Cu having a lower electrical resistance value thanAl as the wiring material has been considered in recent years. However,Cu becomes oxidized more readily than Al. Accordingly, during thesemiconductor manufacturing process, a Cu wiring layer is covered with alayer constituted of a material that does not contain O₂, e.g., anSiN_(x) layer, to prevent oxidation of the Cu wiring layer by assuringthat it is not exposed to O₂.

When connecting a Cu wiring to another wiring in a semiconductor deviceadopting a multilayer wiring structure, it is necessary to etch theSiN_(x) layer and to form at the SiN_(x) layer a connecting hole such asa via hole through which the Cu wiring layer is exposed. However, a CF(fluorocarbon) processing gas containing O₂ is usually utilized in theplasma etching process during which the SiN_(x) layer is etched. As aresult, the surface of the exposed Cu wiring layer becomes oxidized byO₂ or an oxide compound is formed at the Cu wiring layer during theetching process. Such a reaction product raises the electricalresistance value at the area where the Cu wiring is connected with theother wiring, thereby presenting a problem in that the devicecharacteristics of the semiconductor device are compromised.

An object of the present invention, which has been completed byaddressing the problem of the prior art discussed above, is to provide anew and improved etching method and a new and improved plasma processingmethod that solve the problem above and other problems.

DISCLOSURE OF THE INVENTION

In order to achieve the object described above, in a first aspect of thepresent invention, an etching method for etching an SiN_(x) layerpresent on a Cu layer formed at a work piece placed in a processingchamber by raising to plasma a processing gas introduced into theprocessing chamber, which is characterized in that the processing gascontains a gas constituted of C, H and F and O₂, is provided.

In the etching process implemented by using the gas constituted of C, Hand F according to the present invention, the exposed surface of the Culayer is not oxidized readily. In addition, this effect is sustainedregardless of whether or not O₂ is present. For this reason, even whena, wiring, for instance, is connected at the exposed surface of the Culayer, the electrical resistance value at the connection area is notraised. Furthermore, by adding O₂ into the gas constituted of C, H andF, it becomes possible to even more effectively prevent the oxidation ofthe Cu layer.

The gas constituted of C, H and F should be CH₂F₂, CH₃F or CHF₃.

In addition, it is desirable to add an inert gas into the processinggas. When an inert gas is added into the processing gas, the contents ofthe gas constituted of C, H and F and O₂ can be adjusted as necessary incorrespondence to specific process requirements while maintaining thequantity of the processing gas introduced into the processing chamber ata predetermined level.

Moreover, in a second aspect of the present invention, a plasmaprocessing method comprising a step in which an SiN_(x) layer is etchedby using a photoresist layer having a specific pattern formed therein, astep implemented after the etching step, a step implemented after saidetching step, in which said photoresist layer is ashed and a stepimplemented after said ashing step, in which a plasma process isimplemented on the exposed Cu layer by raising to plasma H₂ introducedinto the processing chamber is provided.

It is to be noted that the exposed surface of the Cu layer may becomeoxidized during the ashing step as well. In addition, if a CF gas isused as the processing gas during the etching step, C (carbon atoms) andF (fluorine atoms) may be injected into the exposed surface of the Culayer. Accordingly, in a third aspect of the present invention, thesurface of the Cu layer is treated with H₂ plasma after the etching stepand the ashing step to deoxidize the oxidized Cu and to remove C and F.As a result, the electrical resistance value at the connection areawhere the Cu wiring is connected to the other wiring is prevented fromincreasing even more effectively.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a plasma processing apparatus inwhich the present invention may be adopted;

FIG. 2 presents schematic sectional views of a wafer before and afterimplementing a process by adopting the etching method according to thepresent invention;

FIG. 3 presents schematic diagrams to facilitate an explanation of animplementation example of the etching method according to the presentinvention; and

FIG. 4 presents schematic diagrams to facilitate an explanation of theimplementation example of the etching method according to the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

The following is a detailed explanation of a preferred embodiment of theetching method and the plasma processing method according to the presentinvention, given in reference to the attached drawings.

(1) Etching Method

First, the etching method adopted in the embodiment is explained.

(a) Overall Structure of Etching Apparatus

First, in reference to FIG. 1, a brief explanation is given on a plasmaprocessing apparatus 100 that may adopt the etching method achieved inthe embodiment. A processing chamber 102 is formed in an airtightprocessing container 104. A magnet 106 is provided around the processingcontainer 104 so as to form a rotating magnetic field inside theprocessing chamber 102. In addition, a lower electrode 108 on which aworkpiece such as a semiconductor wafer (hereafter referred to as a“wafer”) W may be placed is provided inside the processing chamber 102.An upper electrode 110 is provided to face opposite the mounting surfaceof a lower electrode 108 in the processing chamber 102.

Numerous gas outlet holes 110 a are formed at the upper electrode 110.The gas outlet holes 11Oa are connected with first˜third gas supplysources 124, 126 and 128 respectively via first˜third switching valves112, 114 and 116 and first˜third flow regulating valves 118, 120 and122. CH₂F₂, O₂ and Ar constituting the processing gas used in theembodiment are respectively stored in the first˜third gas supply sources124, 126 and 128. This structure allows the processing gas constitutedof CH₂F₂, O₂ and Ar individually set at predetermined flow rates to beintroduced into the processing chamber 102 via the gas outlet holes 110a. It is to be noted that the etching process implemented by using theprocessing gas is to be detailed later.

In addition, the processing gas introduced into the processing chamber102 is raised to plasma when high frequency power output from a highfrequency source 130 is applied to the lower electrode 108 via a matcher132. The gas inside the processing chamber 102 is evacuated via a baffleplate 134 provided around the lower electrode 108 and an evacuating pipe136. It is to be noted that the plasma processing apparatus 100 assumesa structure which allows it to perform an ashing process and a surfacetreatment on a Cu layer 204 to be detailed later as well as the etchingprocess.

(b) Etching Process

Next, in reference to FIGS. 1 and 2, a detailed explanation is given onthe etching process implemented on the wafer W by using the processinggas in the embodiment. It is to be noted that FIG. 2(a) presents aschematic sectional view of the wafer W in the state before an SiN_(x)layer 206 is etched. FIG. 2(b) presents a schematic sectional view ofthe wafer W in the state after the SiN_(x) layer 206 is etched.

As shown in FIG. 2(a), the Cu layer (Cu wiring layer) 204 is formed at afirst SiO₂ layer 200 via a TaN layer 202 which functions as a barriermetal layer. In addition, the SiN_(x) layer 206 which is to undergo theetching process in the embodiment is formed on the Cu layer 204 toprevent the oxidization of the Cu layer 204. A second SiO₂ layer 208 tobe used as a layer insulating film and a photoresist layer 210 having aspecific pattern formed therein are sequentially laminated over theSiN_(x) layer 206.

The etching process is implemented in the embodiment after forming a viahole 212 which reaches the SiN_(x) layer 206 is formed at the secondSiO₂ layer 208 through a specific type of etching process as shown inFIG. 2(a). Namely, the processing gas introduced into the processingchamber 102 to etch the second SiO₂ layer 208 is first switched to theprocessing gas constituted of CH₂F₂, O₂ and Ar which characterizes theembodiment. At this point, the flow rate ratio (CH₂F₂/O₂/Ar) of CH₂F₂,O₂ and Ar is set at, for instance, 10 sccm˜30 sccm/10 sccm˜30 sccm/100sccm˜200 sccm. The pressure inside the processing chamber 102 may be setat, for instance, 30 mTorr˜100 mTorr. Then, high frequency power havinga frequency of, for instance, 13.56 MHz and achieving a 300 W˜1000 Wlevel is applied to the lower electrode 108.

Such high frequency power application causes the processing gas todissociate to generate plasma. As a result, the SiN_(x) layer 206becomes etched by the plasma and the upper surface of the Cu layer 204becomes exposed at the bottom of the via hole 212 as shown in FIG. 2(b).Since the SiN_(x) layer 206 has been etched by using the processing gasconstituted of CH₂F₂, O₂ and Ar, the surface of the Cu layer 204 ishardly oxidized during this process, as explained later in reference tosubsequent implementation examples.

(c) Implementation Example

Next, an example of actual implementation of the embodiment is explainedin reference to FIG. 3 and FIG. 4. It is to be noted that FIGS. 3(a) and(b) and FIGS. 4(a) and (b) each schematically illustrate therelationship between the depth measured from the surface of the Cu layer204 and the content of the elements present in the Cu layer 204 at thecorresponding depth. The Cu layer 204 was gradually etched by sprayingAr at a predetermined pressure on to the exposed surface of the Cu layer204.

In the implementation example, the SiN_(x) layer 206 at the wafer Wshown in the FIG. 2(a) was etched by employing the plasma processingapparatus 100 explained earlier. The flow rate ratio of the constituentsin the processing gas was set at CH₂F₂/O₂/Ar=20 sccm/10 sccm/100 sccm.In addition, the pressure inside the processing chamber 102 was set at50 mTorr. High frequency power with a frequency set at 13.56 MHz andachieving a 500 W level was applied to the lower electrode 108. Theresults presented in FIG. 3(a) were achieved by etching the wafer underthe conditions described above. As shown in FIG. 3(a), the Cu layer 204was hardly oxidized when the process was implemented by using theprocessing gas constituted of CH₂F₂, O₂ and Ar, with hardly any C and Finjection observed. Thus, we may conclude that the processing gas iseffective in preventing damage to the Cu layer 204.

Next, as an example that provides a comparison to the implementationexample described above, an etching process was implemented by using aprocessing gas constituted of CF₄ and Ar, and the results presented inFIG. 3(b) were obtained. It is to be noted that the processing gasconstituted of CF₄ and Ar is normally used in an etching processimplemented on the SiO₂ layer 208 or the SiN_(x) layer 206. The flowrate ratio of the constituents of the processing gas was set atCF₄/Ar=20 sccm/100 sccm. Otherwise, the process was implemented underthe same processing conditions as those described above. As shown inFIG. 3(b), when the processing gas constituted of CF₄ and Ar was used,the Cu layer 204 became oxidized to a greater depth and a greater degreeof injection of C and F was observed compared to the extent of oxidationand C/F injection observed in the etching process implemented by usingthe processing gas constituted of CH₂F₂, O₂ and Ar described earlier.Thus, one may conclude that the Cu layer 204 becomes damaged morereadily when the processing gas constituted of CF₄ and Ar is used.

In addition, an etching process was implemented by using a processinggas constituted of CH₂F₂, N₂ and Ar achieved by mixing N₂ instead of O₂,in order to ascertain the extent of the influence of O₂ present in theprocessing gas, and the results presented in FIG. 4(a) were achieved. Itis to be noted that the flow rate ratio of the constituents of theprocessing gas was set at CH₂F₂/N₂/Ar 20 sccm/10 sccm/100 sccm as in theprocessing gas constituted of CH₂F₂, O₂ and Ar. The process wasimplemented by setting the other processing conditions identically tothose described earlier. As shown in FIG. 4(a), the Cu layer 204 becameoxidized to an even further depth and a greater degree of C/F injectionwas observed when the processing gas constituted of CH₂F₂, N₂ and Ar wasused compared to the extent of the oxidation and the C/F injectionobserved in the process implemented by using the processing gasconstituted of CH₂F₂, O₂ and Ar and the process implemented by using theprocessing gas constituted of CF₄ and Ar. This demonstrates that thepresence Of O₂ in the processing gas constituted of CH₂F₂, O₂ and Ardoes not adversely affect the Cu layer 204 but rather, it effectivelyprotects the Cu layer 204.

It is to be noted that the results presented in FIG. 4(b) were achievedby performing a similar measurement on the Cu layer 204 exposed to theatmosphere without implementing the etching process.

As described above, by etching the SiN_(x) layer 206 covering the Culayer 204 with the plasma generated from the processing gas constitutedof CH₂F₂, O₂ and Ar, it is possible to minimize the extent of oxidationof the exposed Cu layer 204 and to reduce the extent to which C and Fconstituting the CH₂F₂ are injected into the Cu layer 204. As a result,the electrical resistance value at the connection area does not increaseeven when another wiring is connected to the exposed surface of the Culayer 204.

(2) Ashing Method

Next, a method that may be adopted to implement an ashing process on thephotoresist layer 210 formed at the wafer W is explained. During theprocess for manufacturing a semiconductor device, an ashing process isnormally implemented after the etching process to remove the photoresistlayer 210 used as an etching mask. However, there is a risk of the Culayer 204 which has not been oxidized during the etching processbecoming oxidized during the ashing process implemented by adopting themethod in the prior art. Accordingly, it is desirable to implement anashing process through the following method on the wafer W that includesthe Cu layer 204.

Namely, following the etching process described above, the temperatureof the wafer W remaining on the lower electrode 108 is sustained at 100°C. or lower and preferably at 40° C. The temperature of the wafer W isadjusted by a temperature control mechanism (not shown) internallyprovided at the lower electrode 108. In addition, a processing gasconstituted of, for instance, O₂, is introduced into the processingchamber 102 at a flow rate of 200 sccm. Then, high frequency power witha frequency of 13.56 MHz and achieving a level of 1000 W is applied tothe lower electrode 108. Through this power application, the processinggas is raised to plasma and thus, the photoresist layer 210 at the waferW shown in FIG. 2(b) is removed.

In this method, the ashing process is implemented while sustaining thetemperature of the wafer W at 100° C. or lower and, as a result, thedegree to which the Cu layer 204 is oxidized is minimized. Thus, thestate of the Cu layer 204 after the ashing process remains essentiallyunchanged from the state following the etching process.

(3) Method of Treating Surface of Cu Layer (H₂ Plasma Process)

Next, a method that may be adopted to treat the surface of the Cu layer204 is explained. It is difficult to completely prevent the oxidation ofthe Cu layer 204 and the entry of C and F even when the process isimplemented by adopting the etching method and the ashing methoddescribed above. Accordingly, it is desirable to implement the followingsurface treatment on the Cu layer 204.

Namely, after the etching process and the ashing process describedabove, the processing gas introduced into the processing chamber 102 isswitched to H₂ with the wafer W still remaining inside the processingchamber 102. The flow rate of H₂ may be set at, for instance, 200 sccm.In addition, the pressure inside the processing chamber 102 may be setat, for instance, 50 mTorr. Then, H₂ plasma is generated inside theprocessing chamber 102 by applying 1000 W high frequency power with itsfrequency set at, for instance, 13.56 MHz to the lower electrode 108.The H₂ plasma thus generated deoxidizes the Cu layer 204 which has beenoxidized. At the same time, the Cu layer 204 is subject to ion implant,which eliminates C and F having been injected into the Cu layer 204during the etching process. As a result, a Cu layer 204 which does notcontain O (oxygen atoms), C and F can be formed.

In addition, the relationship between the depth measured from thesurface of the Cu layer 204 and the contents of O, C and F contained inthe Cu layer 204 at the corresponding depth was ascertained with regardto the Cu layer 204 before and after the H₂ plasma process. The resultsindicate that the contents of O, C and F up to 30 Å from the surface ofthe Cu layer 204 became greatly reduced after the process.

Furthermore, the surface of the Cu layer 204 can be treated by utilizingthe plasma processing apparatus 100 employed to implement the etchingprocess and the ashing process when the method described above isadopted. This means that the surface of the Cu layer 204 does not needto be treated by employing another processing apparatus. Thus, theindividual processes can be continuously performed on the plasmaprocessing apparatus 100 to achieve an improvement in the throughput anda reduction in the production costs.

While the invention has been particularly shown and described withrespect to the preferred embodiment thereof by referring to the attacheddrawings, the present invention is not limited to these examples and itwill be understood by those skilled in the art that various changes inform and detail may be made therein without departing from the spirit,scope and teaching of the invention.

For instance, while an explanation is given above in reference to theembodiment on an example in which CH₂F₂ is used as a constituent of theetching processing gas, the present invention is not limited to thisexample and the advantages described above may be achieved by usingCH₂F₂, CH₃F or CHF₃ instead of CH₂F₂.

In addition, while an explanation is given above in reference to theembodiment on an example in which Ar is added into the etchingprocessing gas, the present invention is not limited to this example andit may be effectively implemented by using an inert gas such as Heinstead of Ar or without adding any inert gas.

While an explanation is given above in reference to the embodiment on anexample in which a single plasma processing apparatus is utilized toimplement the etching process, the ashing process and the Cu layersurface treatment, the present invention is not limited to this exampleand it may be also adopted when separate plasma processing apparatusesare employed to perform the individual processes described above.

According to the present invention, the SiN_(x) layer formed on the Culayer can be etched, while minimizing the extent to which other elementsbecome mixed in the Cu layer. In addition, other elements present in theCu layer can be eliminated through the plasma process implemented byusing H₂. As a result any degradation of the Cu layer can be prevented.

Industrial Applicability

As explained above, the present invention may be adopted during theprocess of manufacturing semiconductor devices and, in particular, it isideal in an application in which a plasma process such as etching isimplemented on an SiN_(x) layer formed on a Cu layer.

What is claimed is:
 1. An etching method for exposing a layer of Cu byetching a layer of SiN_(x) on the layer of Cu with an etching gasconstituted of C, H, and F, and O₂, the O₂ suppressing oxidation of thelayer of Cu while the etching of the layer of SiN_(x) occurs, wherein;said gas constituted of C, H, and F is CHF₃.
 2. An etching method forexposing a layer of Cu by etching a layer of SiN_(x) on the layer of Cu,the method, wherein; a step in which a processing gas containing a gasconstituted of C, H, and F, and O₂ is raised to plasma and an SiN_(x)layer on a Cu layer is etched using a photoresist layer having aspecific pattern formed therein, thereby exposing said Cu layer the O₂suppressing oxidation of an exposed portion of the Cu layer while theSiN_(x) layer is etched; and a step in which H₂ is introduced into saidprocessing chamber and an H₂ plasma process is implemented on said Culayer that has become exposed by raising the H₂ to plasma while removingC atoms and F atoms introduced into the Cu layer that has been exposedduring etching.
 3. An etching method according to claim 2, wherein; saidgas constituted of C, H and F is CH₂F₂.
 4. An etching method accordingto claim 2, wherein; said gas constituted of C, H and F is CH₃F.
 5. Anetching method according to claim 2, wherein; said gas constituted of C,H and F is CHF₃.
 6. An etching method according to claim 2, wherein; aninert gas is added into said processing gas.
 7. An etching methodaccording to claim 2, wherein; said photoresist layer is removed duringan ashing step, and wherein said etching step, said ashing step, andsaid H₂ plasma process are implemented inside a single processingchamber.
 8. An etching method according to claim 2, wherein; a stepimplemented after said etching step and before said H₂ plasma processingstep, in which said photoresist layer is ashed.
 9. A method for etchingan SiN_(x), layer on a Cu layer of a workpiece placed inside aprocessing chamber, the method comprising: introducing a processing gascomprising C, H, and F, and O₂ into a processing chamber, the O₂suppressing injection of C atoms and F atoms of the processing gas intoan exposed portion of the Cu layer while the SiN_(x) layer is etched;and raising the processing gas introduced into the processing chamber toplasma to etch the SiN_(x) layer such that a portion of the Cu layer isexposed.
 10. The method of claim 9, wherein processing gas is CH₂F₂. 11.The method of claim 9, wherein the processing gas is CH₃F.
 12. Themethod of claim 9, wherein the processing gas is CHF₃.
 13. The method ofclaim 9, further comprising introducing an inert gas into the processingchamber.
 14. The method of claim 9, further comprising treating theexposed portion of the Cu layer with H₂ plasma by introducing H₂ intothe processing chamber after etching and raising the H₂ to plasma andexposing the exposed portion of the Cu layer to the H₂ plasma removing Catoms and F atoms introduced into the exposed portion of the Cu layerduring etching.
 15. The method of claim 14, wherein etching the SiN_(x)layer comprises providing a photoresist layer having a specific patternon the SiN_(x) layer; and the method further comprises ashing thephotoresist layer after etching the SiN_(x) layer and before treatingthe exposed portion of the Cu layer with H₂ plasma.
 16. The method ofclaim 15, wherein the etching, the ashing, and the treating of theexposed portion of the Cu layer with H₂ plasma are implemented inside asingle processing chamber.
 17. The method of claim 15, furthercomprising setting the workpiece to a temperature less than or equal to100° C. during the ashing step.
 18. A method for etching an SiN_(x)layer on a Cu layer of a workpiece placed inside a processing chamber,the method comprising: introducing a processing gas comprising C, H, andF, and O₂ into a processing chamber, the O₂ suppressing oxidation of anexposed portion of the Cu layer while the SiN_(x) layer is etched; andraising the processing gas introduced into the processing chamber toplasma to etch the SiN_(x) layer such that a portion of the Cu layer isexposed.
 19. The method of claim 18, wherein processing gas is CH₂F₂.20. The method of claim 18, wherein the processing gas is CH₃F.
 21. Themethod of claim 18, wherein the processing gas is CHF₃.
 22. The methodof claim 18, further comprising introducing an inert gas into theprocessing chamber.
 23. The method of claim 18, further comprisingtreating the exposed portion of the Cu layer by introducing H₂ into theprocessing chamber after etching and raising the H₂ to plasma such thatthe exposed portion of the Cu layer is exposed to the H₂ plasma removingC atoms and F atoms introduced into the exposed portion of the Cu layerduring etching.
 24. The method of claim 23, wherein etching the SiN_(x)layer comprises providing a photoresist layer having a specific patternon the SiN_(x) layer; and the method further comprises ashing thephotoresist layer after etching the SiN_(x) layer and before treatingthe exposed portion of the Cu layer with H₂ plasma.
 25. The method ofclaim 24, wherein the etching, the ashing, and the treating of theexposed portion of the Cu layer with H₂ plasma are implemented inside asingle processing chamber.
 26. The method of claim 24, furthercomprising setting the workpiece to a temperature less than or equal to100° C. during the ashing step.
 27. A method for etching an SiN_(x)layer on a Cu layer of a workpiece placed inside a processing chamber,the method comprising: introducing a processing gas comprising C, H, andF, and O₂ into a processing chamber, the O₂ suppressing oxidation of anexposed portion of the Cu layer and suppressing injection of C atoms andF atoms of the processing gas into the exposed portion of the Cu layerwhile the SiN_(x) layer is etched; and raising the processing gasintroduced into the processing chamber to plasma to etch the SiN_(x)layer such that a portion of the Cu layer is exposed.
 28. The method ofclaim 27, wherein processing gas is CH₂F₂.
 29. The method of claim 27,wherein the processing gas is CH₃F.
 30. The method of claim 27, whereinthe processing gas is CHF₃.
 31. The method of claim 27, furthercomprising introducing an inert gas into the processing chamber.
 32. Themethod of claim 27, further comprising treating the exposed portion ofthe Cu layer by introducing H₂ into the processing chamber after etchingand raising the H₂ to plasma such that the exposed portion of the Culayer is exposed to the H₂ plasma removing C atoms and F atomsintroduced into the exposed portion of the Cu layer during etching. 33.The method of claim 32, wherein etching the SiN_(x) layer comprisesproviding a photoresist layer having a specific pattern on the SiN_(x)layer; and the method further comprises ashing the photoresist layerafter etching the SiN_(x) layer and before treating the exposed portionof the Cu layer with H₂ plasma.
 34. The method of claim 33, wherein theetching,the ashing, and the treating of the exposed portion of the Culayer with H₂ plasma are implemented inside a single processing chamber.35. The method of claim 33, further comprising setting the workpiece toa temperature less than or equal to 100° C. during the ashing step.